Bishop Butler objected to Locke's theory of personal identity on the grounds that memory presupposes personal identity. Most of those sympathetic with Locke's account have accepted Butler's criticism, and have sought to devise a theory of personal identity in the spirit of Locke's that avoids Butler's circularity objection. John McDowell has argued that even the more recent accounts of personal identity are vulnerable to the kind of objection Butler raised against Locke's own account. I criticize McDowell's stance, drawing on a distinction introduced by Annalisa Coliva between two types of immunity to error through misidentification.